Project Summary Management of acute postoperative pain is an essential component of perioperative patient care. Despite a heightened awareness and increased efforts, pain after surgery continues to be a significant clinical problem. The long-term goal of this proposal is to identify novel targets for developing effective non-opioid treatments that can greatly reduce pain after surgery. The overall objective of this proposal is to understand the peripheral mechanisms by which muscle injury, in the course of surgery, activates and sensitizes nociceptive pathways, thereby leading to pain after surgery. The central hypothesis is that sustained pain-related behaviors after muscle injury are in part mediated by TRPA1 and its endogenous ligands in deep tissue. The rationale for the proposed research is that a better understanding of the mechanisms and origin of pain after surgery will allow us to develop new and innovative strategies for effective postoperative pain management. To accomplish the overall objective, the following specific aims are proposed: Aim 1. Establish the role of TRPA1 in muscle injury-related pain behaviors, in rodent models of surgery. The working hypothesis is that pharmacological or genetic inhibition of TRPA1 decreases ongoing, spontaneous pain behaviors and pain with activities that result from by muscle injury during surgery. Aim 2. Examine the effects of tissue injury by surgery on the production of endogenous TRPA1 ligands in the incised muscle environment. The working hypothesis of this aim is that endogenous TRPA1 ligands, such as reactive oxygen species and 4- hydroxynonenal, are increased in the wound environment after incision, contributing to activation of nociceptors via TRPA1. Aim 3. Define the role of TRPA1 in surgery-induced sensitization of muscle nociceptors. The working hypothesis of this aim is that nociceptors innervating incised muscle have greater responsiveness to TRPA1 ligands, compared to nociceptors innervating un-injured muscle. It is expected that the proposed research will demonstrate that endogenous TRPA1 ligands and the TRPA1 receptor are responsible for strong activation and sensitization of nociceptive pathways by incision of deep muscle tissues. These results will have an important positive impact, by identifying novel targets for improved treatment of postoperative pain, as well as greatly advancing our knowledge in the field of pain research.